I recently bought a late 70s Schwinn Twin Sport Tandem. The only problem is that on the right side on the front crankset, there is a problem with the pedal. The pedal feels like it oscilates up and down as you ride it. It's the same feeling you get when you ride a bicycle with a bent crank.

I don't think the problem is the crank, it's how the pedal threads into the crank. The pedal doesn't sit square to the crank. It's out at an angle. I took out the pedal and gingerly threaded it back in. Still the same problem. I think someone had cross threaded the pedal into the crank threads at some point.

Is there a fix for this? I might consider replacing the crankset, but I don't know how easy it would be to find a replacement or where to even start.

I've read about but have no experience with HeliCoil inserts as a fix for stripped threads. A larger hole would be drilled, then the HeliCoil inserted, then the pedal screwed into that. Are the pedal threads OK?

Definitely a Helicoil: drill out the old threads, tap the hole with the new oversized threads for the Helicoil insert, thread-in the Helicoil with a little Loctite, and then thread in your pedal: you're done.

If you haven't done it yourself and don't have a drill press or the other tools needed to tap the hole, you would want to have a local machine shop do it for you. It takes about 10 minutes and some of the better bike shops can do it. The concern with your average bike shop is, most are accustomed to working with soft alloy cranks or frame materials, etc..., not the harder steel that may have been used to make your cranks.

Okay, the helicoil looks like something to investigate. I did forget to mention that this is a 10 speed with aluminum cranks. So, maybe that might make it easier to find a shop, since TandemGeek mentioned that familiarity with aluminum might be helpful.